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(#) Invalidating All RecyclerView Data

!!! WARNING: Invalidating All RecyclerView Data
   This is a warning.

Id
:   `NotifyDataSetChanged`
Summary
:   Invalidating All RecyclerView Data
Severity
:   Warning
Category
:   Performance
Platform
:   Android
Vendor
:   Android Open Source Project
Feedback
:   https://issuetracker.google.com/issues/new?component=192708
Since
:   7.0.0 (July 2021)
Affects
:   Kotlin and Java files
Editing
:   This check runs on the fly in the IDE editor
Implementation
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/RecyclerViewDetector.kt)
Tests
:   [Source Code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/RecyclerViewDetectorTest.kt)

The `RecyclerView` adapter's `onNotifyDataSetChanged` method does not
specify what about the data set has changed, forcing any observers to
assume that all existing items and structure may no longer be valid.
`LayoutManager`s will be forced to fully rebind and relayout all visible
views.

(##) Example

Here is an example of lint warnings produced by this check:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~text
src/test/pkg/RecyclerViewTest.java:24:Warning: It will always be more
efficient to use more specific change events if you can. Rely on
notifyDataSetChanged as a last resort. [NotifyDataSetChanged]
    notifyDataSetChanged();
    ----------------------
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here is the source file referenced above:

`src/test/pkg/RecyclerViewTest.java`:
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~java linenumbers
package test.pkg;

import androidx.recyclerview.widget.RecyclerView;
import android.view.View;
import android.widget.TextView;

import java.util.List;

@SuppressWarnings({"ClassNameDiffersFromFileName", "unused"})
public class RecyclerViewTest {
    // From https://developer.android.com/training/material/lists-cards.html
    public abstract static class Test1 extends RecyclerView.Adapter<Test1.ViewHolder> {
        private String[] mDataset;
        public static class ViewHolder extends RecyclerView.ViewHolder {
            public TextView mTextView;
            public ViewHolder(TextView v) {
                super(v);
                mTextView = v;
            }
        }

        public Test1(String[] myDataset) {
            mDataset = myDataset;
            notifyDataSetChanged();
        }

        @Override
        public void onBindViewHolder(ViewHolder holder, int position) { }
    }
}
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

You can also visit the
[source code](https://cs.android.com/android-studio/platform/tools/base/+/mirror-goog-studio-main:lint/libs/lint-tests/src/test/java/com/android/tools/lint/checks/RecyclerViewDetectorTest.kt)
for the unit tests for this check to see additional scenarios.

The above example was automatically extracted from the first unit test
found for this lint check, `RecyclerViewDetector.testClearAllData`.
To report a problem with this extracted sample, visit
https://issuetracker.google.com/issues/new?component=192708.

(##) Suppressing

You can suppress false positives using one of the following mechanisms:

* Using a suppression annotation like this on the enclosing
  element:

  ```kt
  // Kotlin
  @Suppress("NotifyDataSetChanged")
  fun method() {
     notifyDataSetChanged(...)
  }
  ```

  or

  ```java
  // Java
  @SuppressWarnings("NotifyDataSetChanged")
  void method() {
     notifyDataSetChanged(...);
  }
  ```

* Using a suppression comment like this on the line above:

  ```kt
  //noinspection NotifyDataSetChanged
  problematicStatement()
  ```

* Using a special `lint.xml` file in the source tree which turns off
  the check in that folder and any sub folder. A simple file might look
  like this:
  ```xml
  &lt;?xml version="1.0" encoding="UTF-8"?&gt;
  &lt;lint&gt;
      &lt;issue id="NotifyDataSetChanged" severity="ignore" /&gt;
  &lt;/lint&gt;
  ```
  Instead of `ignore` you can also change the severity here, for
  example from `error` to `warning`. You can find additional
  documentation on how to filter issues by path, regular expression and
  so on
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/lintxml.md.html).

* In Gradle projects, using the DSL syntax to configure lint. For
  example, you can use something like
  ```gradle
  lintOptions {
      disable 'NotifyDataSetChanged'
  }
  ```
  In Android projects this should be nested inside an `android { }`
  block.

* For manual invocations of `lint`, using the `--ignore` flag:
  ```
  $ lint --ignore NotifyDataSetChanged ...`
  ```

* Last, but not least, using baselines, as discussed
  [here](https://googlesamples.github.io/android-custom-lint-rules/usage/baselines.md.html).

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